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Wed May 28, 2008 - Northeast Edition
In 2006, Limestone Properties LLC hired TechniVate Company to remove a section of a hill in Avondale, Pa., leveling it to street grade, so that residential and commercial buildings could be built. Extec crushers and screens were used to remove and crush the rock and sand.
In most stone quarries, contractors start at ground level and excavate downward, but for this quarry, contractors would began at the top of a hill and excavate to ground level.
Located near the center of the town, the hill was approximately 110 ft. (33.5 m) high and 20 to 25 acres (8 to 10 ha) at its base.
Contractors had stripped overburden and quarried rock from the hill in the ’80s and ’90s, but none of this had left a major impact. TechniVate’s project, however, would completely level a portion of the hill.
TechniVate subcontracted the rock drilling and blasting to a local contractor. Three Sandvik track drills were used. The blasthole pattern was 8 by 10 by 30 ft. (2.4 by 3 by 9.1 m), which is within the Pennsylvania Department of Environmental Protection (DEP) specified parameters. TechniVate considered that blast design acceptable; however, the rock fragmentation resulted in oversize rock, which jammed the jaw crushers.
Within seven months of beginning the project, TechniVate had removed approximately 400,000 cu. yd. (305,822 cu m) of rock and sand. The company processed this material through two onsite portable crushing-screening systems. There was at least 1.7 million cu. yd. (1.3 million cu m) of rock yet to be excavated for the hill to be brought to specified grade.
Most of the rock excavated at the top fourth of the hill was mica and mica schist. Both rocks are soft and are used for structural fill. For example, they can be used on certain berm construction projects like sanitary landfills.
Mica and mica schist are classified as structural and are marketed to contractors mostly for private construction uses and to the Cherry Island Landfill facility in New Castle County, Del.
The landfill’s owner, the Delaware Solid Waste Authority, is augmenting the landfill’s capacity through increased vertical waste containment. It is building a berm around the perimeter that is 5,280 by 60 ft. The job requires approximately 3 million cu. yd. (2.3 million cu m) of fill. TechniVate anticipates supplying most of the aggregates for the berm.
As the mining descended, sandstone, quartz and schist were found. Sandstone, a sedimentary rock, and quartz, a metamorphic rock, are classified as granular fill, and can be used in many types of construction. In some cases, the rock even complied with PennDOT specifications for road base.
A Los Angeles abrasion test showed the best rock had an average rate of abrasion of 45 percent, placing it within acceptable abrasion limits as specified by PennDOT.
The quarrying phase of the project is expected to take three years.
Three brands of portable crushing screening equipment are being used and Extec comprises four of the six major plants.
The machines’ manufacturer, Extec Screens and Crushers Limited, is owned by the Sandvik Mining and Construction Group of Sandvik AB.
There are two crushing-screening systems, each including a jaw crusher as the primary crusher and a secondary cone crusher with a double deck screen linking the crushers.
System-I includes an Extec C12 jaw crusher with a 48- by 28-in. (122 by 71 cm) opening, and an Extec S-5 screening plant with a double screen box. Each screen is 60 by 96 in. (152 by 244 cm).
System-I does not produce enough rock and sand to meet the demand for them. One reason is, double-shift crushing is not possible because of time restrictions placed by the DEP.
System-II has greater throughput. It includes an Extec S-6 screening plant with a double screen box, which has 60- by 120-in. (152 by 305 cm) screens; an Extec X44 SBS cone crusher (Telsmith 44 SBS) and a bigger capacity jaw crusher with a 48- by 32-in. (122 by 81 cm) opening.
The bigger jaw was added because oversize rocks were causing jams in the Extec C12 jaw crusher. The C12 can handle rock up to 30 in. (76.2 cm), but this quarry had many oversize rocks (36 in. [91 cm]), because of fragmentation during blasting. The oversize rock caused jams and the large jaw crusher was added to prevent them.
“It reduces the occurrences of jamming but there still is one jam experienced a day. Before there were two to three jams,” said Will Mains.
With the bigger jaw crusher’s price tag considerably higher than a new Extec C12+, the company decided to rent it rather than buy it. All the Extec equipment was bought outright, because it will remain in the fleet for use in a new recycling venture TechniVate is launching.
“If we find another quarry like this one, all the equipment will be used there. Nevertheless, we are starting to go into the asphalt paving and concrete recycling business and we certainly need our Extec jaw crusher for doing onsite recycling,” said Donald Taylor, vice president of TechniVate.
Despite its smaller size, the C12 is more than ample for crushing typical quarry-size rock, asphalt paving and concrete pieces, according to the manufacturer.
According to Taylor, the difference in throughput between the two crushers is not exceptional.
While the big jaw is good at processing oversize rock, the company believes it is too time-consuming and expensive to move it from recycling job site to job site.
“In my opinion, the big jaw is very good if it is kept in a quarry. Nevertheless, it costs too much to move it from one site to another. Many recycling projects have small quantities to crush and we could not justify its moving costs. For instance, the C12 plant just returned from crushing only 2,500 tons of concrete, which is a small project,” said Mains.
According to Mains, it takes approximately 1.5 hours to prepare the Extec C12 for transport using one man and one road tractor. The plant has its own bogie, so a lowboy is not needed. After transport, it requires only 1.5 hours at the site to prepare the plant for production.
Mains said that, by comparison, it takes three men a day to prepare the big jaw crusher for transport. Once onsite, three men must spend another day preparing it for production.
In addition, a crane or a large hydraulic excavator must be used to reduce the plant into three transportable components. Three tractors with lowboy trailers must be used to transport the components. Once delivered to the site, a crane or large hydraulic excavator is again needed to reassemble the plant.
Taylor has considered setting up a crushing/screening yard where contractors could dump concrete and asphalt paving, but many contractors prefer to have the portable plants brought to their sites. As fuel prices increase, fewer contractors are willing to haul material to a yard and then haul crushed material back to their job sites.
Extec Portable Screens
Extec portable screens are central to both crushing-screening systems. The screens are known for their high throughput capacities despite their compact size and the plants’ small footprints, according to Extec.
They have a double box screen design. Each box screen can be independently adjusted to a specified slope. The vibration rate, amplitude and speed also are adjustable. This enables the operator to control the rate of undersize that is removed upon first impact on the screen, so the near size goes to the secondary screen box, which is set at a gentler slope. The gentler slope screens out the remaining undersize materials.
Inside a Crushing System
According to TechniVate, the system the company had developed is very efficient.
Blasted rock is fed into the jaw crusher, which sends the crushed rock to the screen.
The undersize (sand) is stacked with the side-delivery conveyor; the wanted aggregate size is stacked by the main conveyor; and the oversize is sent to the closed circuit cone crusher to be crushed again.
After the cone crusher crushes the oversize, it sends the material back to the screen.
The big jaw crusher is fed 36-in. (91.4 cm) minus. The C12 jaw is fed 30-in. (76.2 cm) minus.
In addition to the jaw crusher, system-II includes the Extec S-6 screen and Extec X44 SBS cone crusher. Occasionally, the C12 replaces the big jaw. For example, when the large jaw crusher must be serviced, the C12 replaces it. Despite the big jaw’s capacity, the C12 throughput is only 50 tons (35.4 t) per hour less.
“We use the jaw crushers interchangeably with the S6 screen and X44 SBS cone crusher because it is important to keep system-II running,” said Mains.
Because of the big screen capacity, production is good with either jaw crusher heading system-II, according to TechniVate. The big jaw crusher’s throughput rate is 450 to 550 tph (408 to 499 t) and the C12 jaw crusher’s throughput rate is 450 to 500 tph (408 to 454 t). The crushing rates fluctuate depending on what ratio of rock to sand is fed the jaw crusher. Crushed rock fed the Extec X44 SBS cone crusher from the screen is between 2 and 6 in. (5 and 15 cm), and is reduced to 2-in. (5 cm) minus.
The throughput for the X44 SBS cone crusher is 200 to 250 tph (181 to 227 t) and the screened-products throughput delivers 450 to 550 tph, which includes a 2-in. minus aggregate and 0.25-in. (0.635 cm) sand. The system-I throughput is not as high because the cone crusher production is 100 to 140 tph (91 to 127 t), even though the crushed rock fed it is 5-in. (12.7 cm) minus instead of the 6-in. (15.2 cm) minus fed the X44 SBS cone crusher in system-II.
“The reason we feed a smaller size rock to this cone is the production was too low when feeding it 6-inch minus,” said Mains.
Despite, the bottleneck of the smaller cone, system-I has a throughput of finished products ranging from 250 to 300 tph (227 to 272 t). The Extec S-5 screen handles 375 to 475 tph (340 to 431 t) that is fed from both the jaw crusher and the recirculating crushed rock fed from the cone crusher.
According to Taylor, the equipment has been very satisfactory and he enjoys the quality service he receives from the Extec dealer, Extec Eastern.
“All the equipment has been performing well, but the services we receive from Extec Eastern have been outstanding. We will continue our business relationship with Extec Eastern because of the services and their products. We lose practically no production downtime using Extec equipment because the dealer responds immediately to any plant issues. The high quality services offered by this company are as important as the quality product it is selling,” he said.
Founded in 1991, TechniVate Company of Landenberg, Pa., is a site improvement company that employs 120 people and has 100 pieces of major equipment. It offers many services ranging from preparation of turnkey building sites with erosion control to underground utilities installation to paving roads that are built onsite by company personnel.